Messages in this thread | | | Date | Tue, 8 Nov 2011 15:57:16 -0800 | From | Andrew Morton <> | Subject | Re: Linus GIT - INFO: possible circular locking dependency detected |
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On Sat, 5 Nov 2011 13:31:46 +0400 Vasiliy Kulikov <segoon@openwall.com> wrote:
> (cc'ed Andrew and Alexey) > > On Thu, Nov 03, 2011 at 20:49 +0000, Luis Henriques wrote: > > On Thu, Nov 03, 2011 at 11:57:20AM -0400, Miles Lane wrote: > > ... > > > > I'm hitting the exact same problem, using a minimal .config file (can send > > it if required), by just running "find /". > > > > I have bisected the problem and found that commit > > aa6afca5bcaba8101f3ea09d5c3e4100b2b9f0e5 seems to be the cause of it.
Well, let's tell the -stable maintainer(s?) that aa6afca5bca ("proc: fix races against execve() of /proc/PID/fd**") is known to cause a regression.
> procfs holds sig->cred_guard_mutex to ensure the target's credentials are > not changed. It is held for a little timeslice. From the stack trace I > don't understand how sys_execve() can happen with ->cred_guard_mutex > held: > > static struct dentry *proc_lookupfd_common(struct inode *dir, > struct dentry *dentry, > instantiate_t instantiate) > { > ... > if (lock_trace(task)) > goto out; > > result = instantiate(dir, dentry, task, &fd); > unlock_trace(task); > ... > } > > > static int lock_trace(struct task_struct *task) > { > int err = mutex_lock_killable(&task->signal->cred_guard_mutex); > if (err) > return err; > if (!ptrace_may_access(task, PTRACE_MODE_ATTACH)) { > mutex_unlock(&task->signal->cred_guard_mutex); > return -EPERM; > } > return 0; > } > > proc_lookupfd_common() always exits without ->cred_guard_mutex held. >
Yes, it's a strange trace. udev is a strange thing and can be triggered by the kernel at odd times. I wonder if it's possible that some other process is now synchronously running udevd while holding cred_guard_mutex. That wouldn't show up in the backtrace. But I doubt if lockdep would notice it either...
Either way, it would be prudent to revert aa6afca5bca from mainline if we can't get this fixed up soon.
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